System Boilers: How They Work & Installation Costs [Combi Upgrades…?]

Read our 4 minute guide all about system boilers – we cover how system boilers work so you can understand how they differ from combi’s and then find you the best system boiler to have installed.

If you have a large property currently with a dead or ‘on the blink’ system boiler and aren’t sure if you should replace it with another system boiler or switch to a combi – we have you covered in this guide.

Let’s skip to the chase, if your boiler is broken or beyond economical repair or you have repaired it before and dont want to have to keep forking out for expensive parts and engineers then stop what you’re doing and try Heatable now for a new boiler.

They offer VERY competitive, on screen FIXED prices in 90 seconds, with no personal data required and can fit the boiler the very next day if you get your skates on and order before 3pm today. 

Click here for your fixed price boiler quote – finance available too.

How Does a System Boiler Work?

A system boiler has a water tank or a cylinder that it uses to store water, ready for instant use; rather than heating water ‘on demand’ like a combi.

System boilers are generally fitted into larger properties where there is a greater demand for hot water. So here we mean things like where there is more than one bathroom and where two showers could run at once, along with say kitchen taps or appliances.

The Benefits of System Boilers

Does having a hot water tank or cylinder have advantages and should/can you switch to a combi?

High Hot Water Demand in Large Properties

Ofcourse there are large combi boilers that could handle the demand that a larger properties require. But it comes to a point where it’s actually not worth it. Remember combi boilers heat water on demand, they don’t store water, so let’s say you have 2 showers running and as many taps going, you’re going to need a huge boiler to meet that demand.  

So versus having to install a huge combi boiler to meet that demand you can install a much smaller kW system boiler, that’s the first advantage. That system boiler will heat and then importantly store that hot water ready for use. So instead of buying a huge combi boiler you can simply install a tank for the exact size of your demands. [chances are you will already have a tank/cylinder if you currently have a system boiler fitted now] 

Better Water Pressure 

The next benefit that system boilers have is the water pressure is better. This is because they get their cold water feed directly from the mains.

The difference here is conventional boilers have a water tank typically located in the loft. Meaning, without a pump, the water from them is gravity fed making the water pressure much much lower.

So with system boilers, the fact they are plumbed directly into the mains means the water pressure is far better than a water tank in the loft. Better still, system boilers can be further tweaked by installing pressurised cylinders. 

Old Systems vs New Ones

System boiler aren’t outdated like people they are – if you own a property with high hot water demand [2+ bathrooms] you don’t have to switch to a combi boiler and it’s quite possible, depending on the age and condition of your cylinder that it can be kept and not have to be replaced either. But…

Solely upgrading your boiler from an outdated heating system, like a back boiler or an oil boiler probably won’t turn it into a supercharged machine and that’s purely down to efficiency.

System Boiler Prices

Prices of system boilers vary and the biggest variance in price is the brand. The better brands with the longer warranties and guarantees did tend to cost more. That was until online boiler comparison sites like Heatable started knocking on the door of brands like Worcester Bosch and subsequently now you can get some real deals on new system boilers. 

They offer finance on purchases and the best bit is they will give you a fixed price on the screen after you fill in this simple form [with no personal details required] in 90 seconds. 

Dirt cheap entry level system boilers do start from around £650, so if you are on a budget you still do have a low level brand option. And those boilers will still have a small warranty. But you do get what you pay for with boilers, and as you start to climb the ranks and look at better brands with bigger kW outputs with longer warranties the price will start to head north. Plus if your cylinder is old and in need of an upgrade obviously that will be an additional cost.

Ideally you want a system boiler that has a 5 year warranty and that’s as a minimum. Our advice would be to go through HEATABLE and pick up the 10 year warranty they offer on Worcester, plus working directly with the largest boiler brands they are able to offer the best system boiler prices on the net, making Worcester’s really affordable.

Worcester Bosch System Boiler Prices

System boilers built by Worcester Bosch are some of the most popular on the market, they are nearly every heating engineers ‘go-to’ favourite boiler, based on efficiency and reliability. 

If you’re looking for system boiler installation, the best deals I’ve found on Worcester’s come hands down from Heatable.

Worcester Boiler Model                                Cost

Greenstar 12RI                                                £790

Greenstar 15RI                                                £830

Greenstar 18RI                                                £865

Greenstar 24RI                                                £945

Greenstar 12I                                                   £880

Greenstar 15I                                                   £930

Greenstar 18I                                                   £990

Greenstar 24I                                                   £1,050

Greenstar 30CDi Classic System                 £1,160

Greenstar 35CDi Classic System                 £1,295

System Boiler Installation Costs

A brand new system boiler installation will only cost you about £2,500 and that includes a new cylinder. Compared to a combi boiler install which will start from around £1,795-£2,000.

Obviously the ‘spec’ will play a factor in the price and ofcourse modifications required in your home such as additional pipework or any movements you may want…

Which is why we can’t stress enough that getting a FIXED price is so vital. Grab a competitive fixed price from an online boiler installer, for the whole job, using Heatable.

Are Heat Only & System Boilers The Same Thing?

No they aren’t. A ‘heat only boiler’ often referred to as a conventional or regular boiler, has similarities in that they both have a tank. But the difference is a heat only boiler requires an additional cold water tank as it’s that cold water tank that feeds the hot water cylinder. 

What is the difference between a system boiler and a combi?

A combi requires no storage tank, as it heats hot water on demand [i.e as and when it’s required]. Which is why properties with 2+ bathrooms normally require such a large, [often unnecessarily large], combi boiler, where a ‘standard’ system boiler would be sufficient.

A much smaller system boiler is required to provide a higher volume of hot water as its all stored, compared to a combi boiler. 

So in short, for larger properties you’d require a massive combi boiler to heat water on demand, vs having a much smaller system boiler which doesn’t have to work half as hard as it stores the water ready for instant usage.

Is a System Boiler Better Than a Combi Boiler?

Yes, BUT only if you have the space for a cylinder. 

Why would you install a massive combi boiler vs a normal sized system boiler? 

Well simply you would if you didn’t have space for a cylinder. Make sense? You could be fully sold on a system boiler and be desperate for one, but not have the space to install the cylinder. 

Typically this is why they are most commonly seen in larger houses not just because of the higher demand for hot water [2 bathrooms etc] but also because there is the space to house the cylinder. 

Hot water cylinders are typically around 150-200 litres and as such will require space to house them. Either in a cupboard or airing cupboard and even under the stairs.

In the average 2-4 bed semi detached house in the UK it might not be possible to fit a cylinder somewhere. 

If you have 2+ bathrooms that is pretty much the prerequisite for requiring a system boiler not a combi – Not always, but mostly.

So after you have done all your demand research and figured out radiator numbers, towel rails, taps and showers it should be plainly obvious whether a system or combi boiler is most suitable. 

The Best System Boilers in 2021

It’s horses for courses, meaning it’s hard to recommend a boiler without knowing the exact spec of your home. 3 beds for instance come in all shapes and sizes, it’s not as simple as saying 2 bathrooms – ok, you need this boiler system…[and let’s face it in some scenarios it could well be more feasible to upgrade to a combi, we aren’t saying it isn’t…]

So rather than running every scenario, taps, rads, towel rails, baths and showers for each home we have created a list of the best boiler brands regardless of whether they are combi or system to help narrow down your selection.

The Best System Boiler Brands

  1. Worcester Bosch [upto 12 year guarantees – they need no introduction]
  2. Viessmann [German brand, so expect efficiency and reliability]
  3. Ideal 
  4. Vailliant
  5. Baxi

What Size System Boiler Do I Need?

Again be wary of anyone who has a specific recommendation for you without asking you some specific questions as there are variables that affect the kW boiler you need and size of system. 

Honestly it is easy to do if you head over and with just a few clicks fill out this boiler size calculator. It takes about 30 seconds and they will give you the best boiler for your home and what fixed price deals there are which include fitting!  

What Cylinder Size Do I Need [+ Cylinder Type]

With cylinders its pretty simple – you either keep your existing one or install a new one. But there are different types of cylinders [just to keep you on your toes!] And it’s pretty crucial you get the right one. Luckily there is only a choice of 2, vented or unvented. And you can probably guess the difference from their name. 

Unvented Hot Water Cylinders – don’t require a water storage tank. So if you have no hot water tank in your home currently you probably have an unvented cylinder. It is fed directly from the mains water supply. So this is ideal for anyone looking to save on space and is a really popular set up. 

Vented Hot Water Cylinder – most commonly found in older properties this system relies on a water storage tank most commonly found in your loft and as such are sometimes referred to as gravity fed hot water systems. 

So in effect you can do away with your vented cylinder and the hot water tank in the loft if you want by installing an unvented cylinder with a system boiler. Get a fixed price for all that here.

What Do I Do Now?

Grab yourself an onscreen fixed price for the exact boiler you require.